Conventionally, an inkjet recording apparatus mainly uses aqueous ink using water-soluble dyes as colorants. However, the dye ink has disadvantages such as poor weather-resistance and poor water-resistance.
Recently, much research has focused on pigment ink that uses pigments in place of water-soluble dyes, and some pigment ink is commercially available. However, pigment ink still has many problems with color development and stability in comparison with dye ink. Particularly, according to technical improvement in OA printers for higher image quality, pigment ink is required to have print quality, hue, color saturation, gloss, and storage stability equal to dye ink on regular papers.
For example, inkjet printing ink is proposed as a low surface tension aqueous pigment ink having a stable ink discharge and improved ink wettability, in which a water-soluble organic solvent, colorants, water, and perfluoroalkylsulfonate are added (see Patent Literature 1). A variety of other ink compositions using fluorochemical surfactants have also been proposed (see Patent Literatures 2, 3, and 4).
However, these proposed compositions all have problems such as poor pigment dispersion stability and poor fixing properties and color development on recording media when the colorants are pigments. Generally, in low surface tension aqueous ink having improved ink wettability, the ink has high foaming properties and easily foams under the influence of surfactants used in the ink, which adversely affects the filling and stable discharge of the ink.
As for color development, C.I. Pigment Red 122 and C.I. Pigment Blue 15:3 are generally used for the pigment ink in magenta and cyan colors, respectively, and have different color reproduction ranges in comparison with dye ink. Toning is used to reduce hue errors. However, reduction in color saturation is inevitable and problems with print quality occur in such a case.
On the other hand, pigments themselves have been modified to change their hue without toning. For example, cyan pigments having hue in the same range as cyan dyes have been proposed in Patent Literature 5 where phthalocyanine pigment having a specific crystalline structure is used. However, they do not satisfy all properties including the problem of cost.
On the other hand, many inkjet recording inks have been proposed in which an ink set comprising pigments as black ink materials and dyes as yellow, magenta, and cyan color ink materials is used (see Patent Literature 6). However, in these proposals, sufficient regular paper properties in printing on regular paper have not been achieved.
According to technical improvements in OA printers for higher image quality, there is an increasing demand in relation to quality, hue, color saturation, and gloss. Particularly, there is an increasing demand for image quality with regard to pigment ink.
Subsequently, a technique is proposed in which a fluorochemical surfactant is contained in the pigment ink to improve wettability on paper, thereby improving color development (see Patent Literature 7). An attempt is made to use silicone resin as the ink-repellent layer of a nozzle head in order to use a fluorochemical surfactant-containing pigment ink having improved wettability.
These proposed techniques allow for improvement in color development of the pigment ink. However, the silicone resin layer as the ink-repellent layer of a nozzle head problematically deteriorates as a result of the elution of its components after it makes contact with the fluorochemical surfactant containing ink.
Therefore, the silicone resin layer is made thicker to ensure ink-repellency even after the components elute from the silicone resin layer of the nozzle head to a certain extent. However, sufficient achievement has not been observed. When the silicone resin layer of the nozzle head is made thicker, it becomes difficult to produce nozzle heads with uniform quality, and it is still difficult to sufficiently function as a nozzle surface (such as stable discharge and cleaning ability).
Hence, there is a high demand for the early providing of a recording ink having improved color development properties ensuring highly stable discharge and excellently uniform solid image parts, and consequently, improved color saturation to form high quality images and, an ink cartridge, ink record, an inkjet recording apparatus, and an inkjet recording method, all using the recording ink.
Patent Literature 1 Japanese Patent Application Laid-Open (JP-A) No. 57-90070
Patent Literature 2 Japanese Patent Application Laid-Open (JP-A) No. 4-211478
Patent Literature 3 Japanese Patent Application Laid-Open (JP-A) No. 5-230409
Patent Literature 4 Japanese Patent Application Laid-Open (JP-A) No. 6-200200
Patent Literature 5 Japanese Patent Application Laid-Open (JP-A) No. 2000-17207
Patent Literature 6 Japanese Patent Application Laid-Open (JP-A) No. 2000-239590
Patent Literature 7 Japanese Patent Application Laid-Open (JP-A) No. 2003-335987